Master student T.A. Zemlyanukhina¹
PhD, Associate Professor T.V. Rybyakova²
Master student E.Yu. Podyacheva¹
Dr. Biol. T.I. Baranova^1
1 Saint Petersburg State University, St. Petersburg
²Lesgaft National State University of Physical Education, Sport and Health, St. Petersburg

Keywords: synchronized swimmers, diving reflex, cardiovascular system, body functional reserves.

Background. The activities of synchronized swimmers are characterized by a number of physiological features that distinguish them from the dry land activities. Water is a powerful irritant of the thermal and tactile skin receptors. Facial and neck skin are particularly sensitive to its effects. When these body parts are submerged in the water, a powerful chain of inherent reflex cardiovascular reactions, the so-called diving reflex, is activated [4]. The diving reflex during submersion is accompanied by the activation of the cold and tactile receptors. From them, on the afferent pathways of the facial and triple nerve, the signals are transmitted to the X pair of the cranial nerves, and from them - to the sinus node of the heart, which results in a reflex decrease of the heart rate, sometimes a decrease in the stroke volume, with a reduction of the minute blood volume. At the same time, the signal is transmitted from the vasomotor center of the oblongata brain through the sympathetic nerve fibers of peripheral vessels, causing the constriction of the skin vessels, inactive muscle vessels, vessels of the gastrointestinal tract and abdominal cavity (see Figure 1).

Fig. 1. Dynamics of blood flow when diving on the example of testee I.K.

ECG – electrocardiogram, IRG – integral rheogram, PPG – photoplethysmogram, RVG – rheovasogram, d index – differential of corresponding rheogram, Т_apneic – diving time.

These reactions are amplified if immersion is associated with breath-holding, drop in the partial pressure of oxygen, and accumulation of carbon dioxide in the blood and tissue. At the same time, the blood flow is selectively redistributed from oxygen-resistant organs to the heart and brain, which have no tolerance to hypoxia [4]. Therefore, oxygen consumption is reduced in terms of oxygen deficiency. In other words, this series of responses perform a protective function. However, due to high energy consumption physical loads are accompanied by intensive oxygen consumption. On dry land, this entails mobilization of the cardiorespiratory system: an increase in heart rate, stroke volume, breathing rate and depth. There is a conflict - an inherent reflex aimed to save oxygen (reflex bradycardia, constriction of blood vessels) and strenuous physical work require additional oxygen supply and hence mobilization of the gas transport systems. How does the body react to these conditions? Let us take the example of the female synchronized swimmers.

Objective of the study was to identify the features of diving reflex in synchronized swimmers.

Methods and structure of the study. Sampled for the study were 36 female synchronized swimmers of different sport qualifications (masters of sport aged 15-17 years old and first-rank athletes 12-14 years old). Their cardiovascular indices were analyzed. The manifestation of the diving reflex response can be evaluated by immersing the face in the water. This makes it possible to conduct an in-house study using a simulated diving model [1, 2]. The subjects were to lay down on their stomachs, hold their breath, and immerse their faces in the water. The water and air temperatures were close to the swimming pool conditions and amounted to 27±1.3°C and 26±2.1°C, respectively. Heart rate was measured in the pool with the head fully immersed in the water by the method of radiopulsometry using PolarTeamSystem transmitters. In the laboratory conditions, during the rest pause, during the simulated diving test, and during the recovery period after the test, we measured the subjects' stroke volume (SV, mg) and minute blood volume (MBV, l) using Tishchenko's integral rheography, and systolic wave amplitude (SWA, pm) distal phalanx of the hand, which indirectly reflects the peripheral vascular tone, using photoplethysmography. We also registered ECG in the standard leads and blood pressure (BP) rates. The ECG indicators were used to determine the type of diving response by the method developed by T.I. Baranova [2]. The following indicators were considered: latent period of reflex bradycardia (when the RR interval during the face immersion in the water exceeded the maximal baseline value - L, sec); degree of bradycardia (ratio between maximal RR interval during immersion and maximal baseline RR interval - DB, c.u.); time of onset of the maximal RR interval during immersion - t (sec). We recorded the breath holding time during immersion- T (sec). Based on these indicators, we determined the type of cardiovascular system response: high-reactive type - the latent period of bradycardia L<9sec, DB>1.25, t - close to the end of apnea; reactive type - the latent period of bradycardia L>9sec, DB>1.11, t - can appear in the middle of apnea; paradoxical type - the increase of heart rate during immersion, DB<0.89. The body's reaction to immersion is similar to its reaction to stress. The areactive type - there is no bradycardia, 1.1<DB>0.9.

Blood saturation was determined by the method of pulse oximetry (using the pulse oximeter by "Mizar").

The Wilcoxon and Mann-Whitney non-parametric methods were used to assess the statistical significance of the changes. The correlation analysis was conducted using the Spearman’s correlation method.

Results and discussion. The deceleration of heart rate and peripheral vessel constriction, as well as increased blood pressure during submersion depend on the reactivity of the autonomic nervous system, adaptability to work in the water (diving and swimming), as well as on the genetic features of the body [3].

Diving reflex in the female synchronized swimmers. The comparative analysis of the changes in heart rate of the female athletes in the laboratory conditions and in the swimming pool with the complete submersion failed to reveal any differences.

The duration of apnea during simulated diving was on the average 83.6±23.9 sec per group. The analysis of the deceleration of heart rate during submersion showed that the latent heart rate deceleration period was longer in the masters of sport than in the untrained females. The percentage of females with the areactive type of response was higher among the synchronized swimmers than among the untrained females. For example, the percentage of the female athletes with the areactive type of response was 40%, with the reactive type - 50%, with the high-reactive type - 6.7%, with the paradoxical type - 3.3%, while among the untrained females, the percentage ratio was as follows: 13-15%, 45-55%, and 3.5-5%, respectively. At the same time, in the group of first-rank female athletes, the percentage ratio of response types was slightly different: high-reactive type - 30%, reactive type - 40%, areactive type - 20%, and paradoxical type - 10%. The correlation analysis revealed a direct correlation between the apneic time, latent period, and the time of onset of the peak RR interval during submersion (CC=0.88, p<0.01). There was an inverse correlation between the degree of bradycardia and apneic time (CC=0.68, p<0.01). Therefore, the stronger the cholinergic effect decelerating heart rate, the shorter the apneic time during simulated diving.

The most pronounced decrease in SpO₂ was observed in the female athlete with the paradoxical type of response (with the predominance of adrenergic effects on the heart): the 53-sec apnea led to a decrease in oxygen saturation to SpO₂=84%. While in the female athlete with the areactive type of response, the 71-sec apnea led to a decrease in oxygen saturation to SpO₂=94%.

Peripheral blood flow during simulated diving. All female athletes were found to have a decrease in the systolic wave amplitude, reflecting the blood filling in peripheral vessels. The decrease in the systolic wave amplitude in the first-rank female athletes was significantly greater (p<0.01) than in the masters of sport. The systolic wave amplitude rates at rest and during submersion were as follows: first-rank female athletes - 0.82±0.21 and 0.26±0.07, masters of sport - 0.87±0.13 and 0.53±0.03, untrained females - 0.74±0.15 and 0.33±0.04, respectively.

The blood pressure increase during simulated diving. One of the differences in human diving is the blood pressure increase. At the same time, in some individuals, blood pressure increases by 10-15 mmHg, in others - by 80-100 mmHg. The increase in blood pressure during diving is a consequence of peripheral vasospasm. It should be noted, however, that in the masters of sport the blood pressure increase, as well as the narrowing of peripheral vessels, was less pronounced than in the first-rank female athletes (see Table 1).

Table 1. Blood pressure changes in the female synchronized swimmers (first-rank and masters of sport) during simulated diving

Conclusions. We detected an inverse high correlation between the apnea duration, degree of bradycardia, and rate of its increase during immersion. Considering that the breathhold duration in synchronized swimming and the ease with which it is tolerated is essential for the performance of figures, it can be concluded that the most favorable type of reaction in this sport is an areactive one, characterized by a slight deceleration of heart rate and moderate constriction of the peripheral vessels. Although the diving reflex performs a protective function during immersion, thus contributing to the economical oxygen consumption and preservation of the cerebral blood flow, during short-term immersion the strong vagal effects on the cardiac function realized at the moment of immersion and slowing down of the blood flow hindered mobilization of the body functional reserves. This may adversely affect the competitive results. Is the type of response innate? Or can it change in the training process? Our long-term observations showed that, in 75% of synchronized swimmers with the high-reactive type of cardiovascular system response, reactivity decreases due to trainings. In 25%, the type of reactivity is preserved throughout life. There was also a case of neutralization by the sympathetic nervous system of adverse vagal effects on the heart of the female athlete with the high-reactive type of cardiovascular system response (paradoxical type of response). In other words, a stress reaction to diving is developed. This type of response is not beneficial since it increases hypoxic loading. At the same time, observations revealed that such compensation can lead to neurogenic hypertension over time.

We assume that the type of cardiovascular system response to diving should be considered in the sports selection for synchronized swimming.

References

1. Andersson J., Liner V.Y., Fredsted A., Schagatay K.A. Cardiovascular and respiratory responses to apneas with and without face immersion in exercising humans. J Appl Physiol. 2004. no. 96. pp.1005-1010.
2. Baranova T.I. Characteristics of the human cardiovascular system in the human diving response. Russian J. of Physiology. 2004. No. 90(1). pp. 20-31.
3. Baranova T.I., Berlov D.N., Glotov O.S. et al.  Genetic determination of the vascular reactions in humans in response to the diving reflex. Am J Physiol Heart Circ Physiol. 2017. No. 312 (3). pp. 622–631.
4. Gooden B.A. Mechanism of the human diving response. Integrative physiological and behavioral science. 1994. No. 29(1). pp.6-16.

Corresponding author: baranovati@gmail.com

Abstract

Objective of the study was to identify the features of diving reflex in synchronized swimmers.
Methods and structure of the study. Sampled for the study were 36 female synchronized swimmers of different sport qualifications (masters of sport and first-rank athletes). Their cardiovascular indices were analyzed.

Results and conclusions. We detected an inverse high correlation between the apnea duration, degree of bradycardia, and rate of its increase during immersion. Considering that the breathhold duration in synchronized swimming and the ease with which it is tolerated is essential for the performance of figures, it can be concluded that the most favorable type of reaction in this sport is an areactive one, characterized by a slight deceleration of the heart rate and moderate constriction of the peripheral vessels. Although the diving reflex performs a protective function during immersion, thus contributing to the economical oxygen consumption and preservation of the cerebral blood flow, during short-term immersion the strong vagal effects on the cardiac function realized at the moment of immersion and slowing down of the blood flow hindered mobilization of the functional reserves of the body. This may adversely affect the competitive results.

Therefore, the optimal type of cardiovascular response to diving in synchronized swimming was identified. The authors propose that evaluation of the cardiovascular response to diving should be included in the sports selection for synchronized swimming.